Project Summary/Abstract Natural products account for two-thirds of the antibacterial pharmacopeia and are therefore privileged scaffolds. These complex molecules have inspired novel synthetic methods and positively impacted the fields of biochemistry, molecular biology, and medicine. The proposed project is inspired by albocycline, a unique 14-membered macrolactone with potent, narrow-spectrum activity against the ?superbug? methicillin- resistant Staphylococcus aureus (MRSA). We have validated that albocycline is effective against MRSA and vancomycin-resistant S. aureus strains; moreover, it is non-toxic to human cells. In 2013, Tomoda reported that albocycline inhibited peptidoglycan (i.e., bacterial cell wall) synthesis in macromolecular assays. Using biochemical assays and molecular modeling, we demonstrated that albocycline was a weak (mM) inhibitor of MurA from S. aureus. Consistent with its narrow-spectrum profile, albocycline did not inhibit MurA from E. coli. Based on our results and those of Tomoda, we conclude it must have additional bacterial targets. Significantly, we recently completed a modular, step-efficient total synthesis of the natural product driven by novel chemistry of N-sulfinyl metallodienamines. Accordingly, in Aim 1 we propose to prepare albocycline analogs (including probes) by semi- and diverted total synthesis to explore the chemical space about this privileged scaffold. In Aim 2, we will co-crystallize albocycline in complex with MurA based on exciting preliminary results and employ structure-based analog design. We will also identify the target(s) of albocycline to determine its mode-of-action using computational chemistry, chemical proteomics and genomics approaches, in addition to a novel metabolic labeling methodology. Finally, in Aim 3 we will evaluate the biological activity of all albocycline analogs. At the end of the four-year project period, we will have (1) a deeper understanding of how albocycline exerts its antibacterial action; (2) a library of tool compounds and antibiotic lead candidates that selectively modulate their target(s); and most significantly, (3) a bona fide launching point for the development of novel, narrow-spectrum antibiotics to treat recalcitrant MRSA, VISA, and VRSA (i.e., the project's long-term goal).